Retry http failures in ServiceAccountCredentials.refreshAccessToken

[garrettjonesgoogle]

As reported in googleapis/google-cloud-java#1545 , users have seen failures in ServiceAccountCredentials.refreshAccessToken, which has no retries on the http call. These failures should be retried.

java.io.IOException: Error getting access token for service account:
         at com.google.auth.oauth2.ServiceAccountCredentials.refreshAccessToken(ServiceAccountCredentials.java:319)
         at com.google.auth.oauth2.OAuth2Credentials.refresh(OAuth2Credentials.java:149)
         at com.google.auth.oauth2.OAuth2Credentials.getRequestMetadata(OAuth2Credentials.java:135)
         at com.google.auth.http.HttpCredentialsAdapter.initialize(HttpCredentialsAdapter.java:96)
         at com.google.cloud.HttpServiceOptions$1.initialize(HttpServiceOptions.java:224)
         at com.google.api.client.http.HttpRequestFactory.buildRequest(HttpRequestFactory.java:93)
         at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(AbstractGoogleClientRequest.java:423)
         at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(AbstractGoogleClientRequest.java:352)
         at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.execute(AbstractGoogleClientRequest.java:469)
         at com.google.cloud.storage.spi.DefaultStorageRpc.create(DefaultStorageRpc.java:245)
         ... 10 more
 Caused by: java.net.SocketTimeoutException: connect timed out
  ...

[tcoffee-google]

Following testing investigations: Due to the limitations of various mechanisms available for dealing with timeouts in this context, it looks as though it will be exceedingly complicated to configure retrying in a way that's reliably compatible with the retrying specification used in GAX. Thus, for this use case, I'm planning to abandon this approach and instead use the distinct retrying functionality native to google-http-java-client.